Cellular and other portable radio telephones typically have antennas which extend from the housing of the phone. While the phone is in use the antenna emits radiation which has caused concern among the medical community as to the radiation's effects on the user of the phone.
The use of flexible protective shields to protect personnel against X-ray frequency and Gamma frequency radiation such as may be emitted by X-ray machines or by nuclear reactors, respectively, is known in the art as illustrated by U.S. Pat. No. 3,039,001 entitled "Flexible Protective Plastic Shield" and by U.S. Pat. No. 5,012,114 entitled "Radiation Shield".
U.S. Pat. No. 3,039,001 discloses that a sheet of vinyl or other plastic material containing resin, plasticizer and stabilizer may have a protective material such as pulverized lead uniformly distributed therethrough in order to provide a flexible sheet of material which protects the wearer against X-rays, Gamma rays, Neutron rays, secondary cosmic rays and the like.
U.S. Pat. No. 5,012,114 discloses a gamma radiation shield which comprises a wrappable sheet of gamma radiation shielding material to which is affixed releasable contact-fasteners, which are so dimensioned and configured that when a shield member is wrapped around a gamma radiation emitting structure, complimentary locking portions of the releasable fasteners engage each other to securely hold the shield member in shielding position wrapped around the structure. The gamma radiation shielding material may be comprised of the known construction of fine lead powder being uniformly dispersed in a matrix of thermo-plastic material which serves as a binder for the lead powder so as to form a flexible sheet. The releasable contact-fasteners may be of a type sold under the trade-mark Velcro. The patent is directed to protecting personnel in nuclear reactors and the like by shielding conduits such as pipes, most clearly seen in FIG. 6 of the patent, through which radioactive material flows.
The use of electromagnetic shielding to minimize interference between electromagnetic signals radiated by cellular phones and like electronic equipment with another portion of that equipment and the minimization of such interference by interposing electrically conducting material in the form of a shield between the source of the electromagnetic signals and the circuitry subject to interference is taught by U.S. Pat. No. 5,124,889 entitled "Electromagnetic Shielding Apparatus for Cellular Phones". The reference to electromagnetic shielding does not appear to be concerned with protecting the user of the electronic device from radiation from the antenna or the like.
With portable radio telephones such as hand-held cellular phones, radio waves that carry the call emanate directly from the telephone, specifically the length of the telephone and antenna, most intensely at a midpoint there along, while the telephone is held to the ear of the user. There is concern that the radio frequency waves entering the dissipative medium of the user's head may cause heating, cancer or DNA fragmentation.
There is currently being marketed a cellular phone radiation shield being sold under the trade-mark "Cellguard", manufactured by Quantum Laboratories of Renton, Wash., U.S.A. As discussed in more detail below, the "Cellguard" device consists of two sections of molded plastic, each with metal inside, that serves to block or deflect the radio frequency signal. One part of the device covers the phone's antenna and the other part fits over the earpiece of the phone. The metal of the Cellguard device is placed between the antenna and the user and between the earpiece and the user. A similar device, that is, an arrangement in which a radiation shielding device is placed between the antenna and the user is taught in U.S. Pat. No. 5,335,366 which issued to Daniels on Aug. 2, 1994. In particular, Daniels discloses a radiation shielding apparatus for a radio transmitting device having a radiation shield disposed between the antenna and a user, the radiation shield for absorbing, blocking and/or reflecting electromagnetic wave radiation.
U.S. Pat. No. 5,336,896 which issued to Katz on Aug. 9, 1994 for a cellular telephone users protective device teaches a cellular telephone accessory both for protecting a user from electromagnetic radiation and for providing a handle for the cellular phone. In particular, a tilt and swivel base is taught to permit moving the cellular phone antenna away from close contact with the user's head and to also supply a carrying handle. What is further taught is providing a protective magnetic radiation shielded jacket to contain the cellular phone within the jacket, the antenna tilt and swivel base attached to the outside of the jacket.
The present invention has at least five objects. The first object, in one embodiment, is to reduce the overall amount of electromagnetic radiation emitted by reducing the emitted power of the antenna. The second object, in a further embodiment, is to redistribute the radiation in the vicinity of the phone and in particular the antenna, ie. in the near field, away from an associated dissipative medium such as the head of a user. Consistent with this object, the present invention changes the near field radiation pattern surrounding a radio communication device such as a radio phone, and in particular surrounding the device's antenna so that: (a) a reduction is attained in radiation field strength during transmission thereby reducing "hot spots" at the associated dissipative medium such as the user's head; (b) a reduction is attained in the amount of radiated energy during transmission which is absorbed by the associated dissipative medium, to thereby increase the effective power of the radio transmission; and, (c) an increase is attained in the effectiveness of the antenna during reception of radio transmissions by an increase in the effective exposure of the antenna.
The third object is to accomplish the above objects without significantly adversely affecting the operation of a radio communication device such as a cellular telephone within a cellular telephone communication system, which adverse operation may result if the antenna excessively loses radiating power or becomes excessively directional. In the case of cellular telephones it is desirable that the far field radiation pattern does not have large signal strength variations with the direction in which the signal is sent. It is desired that the user can hold the cellular telephone in a random orientation without concern about the direction in which the signal must travel in order to reach the center of the cell. Modification of an antenna can result in large changes to the far field radiation pattern. Since this is undesirable, it is an object of the present invention to not cause large changes to the far field radiation pattern while at the same time, over the entire desired operational bandwidth, minimizing the near field "hot spots" on an associated dissipative medium where radiation strength is excessive, minimizing the amount of radiation absorbed by the dissipative medium, and maximizing the effective exposure of the antenna to reception of radio transmissions.
The fourth object is to avoid damage or undue strain on the internal electrical circuitry of the cellular phone. Such damage is conceivable in a situation where a modification to the antenna results in a greater electrical load being placed on the electrical circuitry so that a greater current flows through parts of the cellular phone. If this increased current exceeds the limits contemplated by the designers of the cellular phone, some internal parts of the cellular phone could have their operation impaired or could malfunction.
The fifth object is to maintain operation of the receiving function of the cellular telephone to an acceptable degree. The antenna of the cellular telephone simultaneously operates with two functions. One is to transmit signals, and it is this function that results in high intensity radiation being present in the vicinity of the cellular telephone. The second function of the antenna is to receive signals from a distant source, convert these signals into oscillating electrical currents which are converted by the circuitry of the cellular telephone into a voice message heard by the user. It is conceivable that modifications to the antenna could decrease the ability of the cellular phone to clearly receive these incoming signals. It is an object of the present invention to not cause unacceptable reduction in the quality of these incoming signals, but in fact to increase the reception quality by increasing the effective exposure of the antenna.